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emoore924 · Joined: 13 Apr 2004 Posts: 2822

If so, I'd love to know:

1) Did you cut the piston reliefs to accommodate the larger valves?

2) Are you running a high-lift cam? If so, which one, what's the lift and duration, and did that enter into your decision to cut or not to cut above?

3) Are you running stock compression pistons, meaning 8.5:1 USA, 9.3:1 euro, or something else?

4) Are you running a n/a or turbo big valve head?

5) What size valves did you use? Are they 44/37 or something else?

PM if you want to take the discussion offline.

Thanks!

Slam · Posted: Fri Oct 16, 2009 1:33 am Post subject:

Check out all the posts by Chrenan. He did the big valve head and Euro comp pistons with a hotter cam, plus the Audi throttle body. I own the car now and was able to do a direct comparison with my stock 84 Euro 924. My 84 has a snappier throttle and I was able to keep up with my wife driving the big-valve car - to a point. In the upper end the big-valve car is faster, as that's when it comes onto the cam, and I think the emissions equipment between the two cars makes a big difference. The Euro has virtually none, while Chrenan kept the stock emissions on the big-valve car. We haven't lived with Chrenan's old car long enough to really get to know it, though. I think I'll remove the emissions controls from it, retune it and see if I can't squeeze a bit more from it. It's very good as it is, though. I'm impressed with what he did and I'm really happy with the car.
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'88 944 Auto - may or may not resurrect

!tom · Posted: Fri Oct 16, 2009 1:45 am Post subject:

I'm contemplating this too, so I'd like to see the discussion here.

The only one I'm aware of is Chrenan, who documented what he did extensively. However, he's sold his as he likes his 951 better, in spite of his review. Slam is the proud new owner.

Unfortunately, Chrenan had all the details of his modifications in his signature, which he has cleaned up since he no longer owns that car. I believe it was basically removing the cat, the valve job you're talking about, Euro pistons, Audi throttle body, and a Stage 1 cam, from memory.
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78 924 NA
5-lug

emoore924 · Joined: 13 Apr 2004 Posts: 2822

Hey thanks, yeah, I saw that but it didn't seem to address the reliefs + cam + compression question I had...

Joes924Racer · Posted: Fri Oct 16, 2009 3:13 am Post subject:

slam you bought Chrenans car the yellow one with the nice seats and rollbar...i knew about the motor as i was pretty jealous when I found out.
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1979 porsche 924 Na
1980 porsche Turbo 931GT Replica
Have u ever driven a turbo.

!tom · Posted: Fri Oct 16, 2009 3:26 am Post subject:

Slam · Posted: Fri Oct 16, 2009 4:00 am Post subject:

Considering how cheap timing belts for these cars are, I'll be changing it every spring.

Joe, I got the car sans the roll bar and seats, which was fine by me. I've got sports seats for it and the roll bar wasn't an issue. I got what I considered to be a fantastic deal, and to quote a buddy of mine when I told him about it, "It would be un-Christian not to!" Plus, Mand's birthday is just around the corner and I haven't bought her a car in a while.

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'88 944 Auto - may or may not resurrect

emoore924 · Joined: 13 Apr 2004 Posts: 2822

ideola · Joined: 01 Oct 2004 Posts: 15550 Location: Spring Lake MI

Based on the fact that there are reliefs in the NA pistons, and based on the fact that the valves in the EMW head are 4mm bigger, I would say that alone would make it an interference design. Valve reliefs are usually cut very specifically for the valves, and I doubt that they would accommodate an add'l 4mm of diameter.
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erstwhile owner of just about every 924 variant ever made

emoore924 · Joined: 13 Apr 2004 Posts: 2822

Ok, ya, my duh. I think I'm using the wrong terminology.

Let me ask a different way...

How do i figure out whether the valves will or won't hit the pistons given a certain piston configuration, cam profile, valve stem length, stroke and valve head diameter...?

ideola · Joined: 01 Oct 2004 Posts: 15550 Location: Spring Lake MI

Modelling clay?

Seriously, I'm sure there's a mathematical formula, but I don't know what it is

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erstwhile owner of just about every 924 variant ever made

Vince Ponz · Joined: 02 Nov 2002 Posts: 3581 Location: Florida

I have a great mechanic in LI who made all the upgrades on all my cars. Need his number?
He is a Porsche mechanic full time here in LI. He is fanatical about cleanliness and doing the right thing.
He did all the work on my track car as well as the others........all 8 of them.
He also worked for Autosport in LI.
Let me know.
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"Never let them see you sweat"
77.5 924 modified track car
79 931 Euro stock
88 924S SE
87 911 Targa stock